Chloride ions adsorption

This potential depends on the interfacial tension am of a passivated metal/electrolyte interface shifting to the lower potential side with decreasing am. The lowest film breakdown potential AEj depends on the surface tension of the breakdown site at which the film-free metal surface comes into contact with the electrolyte. A decrease in the surface tension from am = 0.41 J m"2 to nonmetallic inclusions on the metal surface, will cause a shift of the lowest breakdown potential by about 0.3 V in the less noble direction. 

Monitoring of Au(l 11) surface changes in dependence on electrode potential and chloride ions adsorption. 

B.E. Wild, Chloride ion adsorption and pit initiation on stainless steels in neutral media, in R. W. Staehle, H. Okada (Eds.), Passivity and its Breakdown in Iron Based Alloys, NACE, Houston, 1976, pp. 129-130. 

A theoretical model to study chloride diffusion in concrete has been developed by Arora and Popov [77]. Two different coordinate systems are considered to model structure geometry. A chloride ion adsorption and diffusion schematic in a one-dimensional concrete cylinder is shown in Fig. 12.6, comparable to a planar slab with one-dimensional chloride diffusion. Chloride ingress follows Pick s law of diffusion for cured concretes [77]. 

Fig. 12.6 Chloride ion adsorption and diffusion schematic in a one-dimensional concrete cylinder [77].

Lj Vracar, D.M. Drazic, Influence of chloride ion adsorption on hydrogen evolution reaction on iron,... 

An important feature of such films is their low ionic conductivity that restricts cation transport through the film substance. Electronic semiconduction, however, permits other electrode processes (oxidation of H2O to O2) to take place at the surface without further significant film growth. At elevated anodic potentials adsorption and entry of anions, particularly chloride ions, may lead to instability and breakdown of these protective films (Sections 1.5 and 1.6). 

Local breakdown of passive film results from a localized increase in the film dissolution rate at the anion adsorption sites that are attacked by chloride ions, as will be discussed later, in the same manner as substrate metal dissolution. Such acceleration of the dissolution rate was ascribed to the formation of metal chlorides24 or the local degeneration of film surface by the formation of surface electron levels.7... 

Macdonald et al.25 28 maintained that the adsorption of chloride ions enhances the formation of cation vacancies of metal ions and their transfer... 

MacDonald on the adsorption of chloride ions in passivation, 237 of CO on electrochemically facetted platinum, 135 of diols on mercury, 188 of neutral compounds on electrodes, 185 of perchlorate ions, copper and, 94 specific adsorption, anodic dissolution and, 256... 

Chromatograms demonstrating the simultaneous use of all three detector functions are shown in figure 22. It is seen that the anthracene is clearly picked out from the mixture of aromatics by the fluorescence detector and the chloride ion, not shown at all by the UV adsorption or fluorescence detectors, clearly shown by the electrical conductivity detector. 

Copper(II) ions in the presence of chloride ions are reduced at the dropping mercury electrode (dme) in two steps, Cu(II) -> Cu(I) and Cu(I) -> Cu(0) producing a double wave at -1-0.04 and 0.22 V versus sce half-wave potentials. In the presence of peroxydisulphate , when the chloride concentration is large enough, two waves are also observed the first limiting current corresponds to the reduction of the Cu(II) to Cu(I) plus reduction of a fraction of peroxydisulphate and the total diffusion current at a more negative potential is equal to the sum of the diffusion currents of reduction of Cu(II) to Cu(0) and of the peroxydisulphate. There is evidence that peroxydisulphate is not reduced at the potential of the first wave because of the adsorption of the copper(I) chloride complex at... 

Deactivation can be understood in terms of the mechanism based on adsorption of the anions. Although a lower current density would need a less positive potential if for example, chloride ions stayed at the surface, as soon as the potential shifts negative, desorption of chloride should take place, with a corresponding loss of activity. 

It is interesting to compare these results with the electrophoretic measurements made under identical electrolyte concentrations. Figure 8 shows that the variation of electrophoretic mobility with sodium chloride concentration is different for the bare and the PVA-covered particles. For the bare particles, the mobility remains constant up to a certain salt concentration, then increases to a maximum and decreases sharply, finally approaching zero. The maximum in electrophoretic mobility-electrolyte concentration curve with bare particles has been explained earlier (21) by postulating the adsorption of chloride ions on hydrophobic polystyrene particles. In contrast, for the PVA-covered particles, the mobility decreases with increasing electrolyte concentration until it approaches zero at high salt concentration. 

The hydration of polyoxyethylene (POE) is dramatically affected by the anion present(J 0) in the aqueous phase. The adsorption of HEC (both 2.0 and 4.3 M.S.) was therefore studied in Na SO and Na PO, at equivalent normalities. The multivalent anions are more effective in precipitating POE than is the chloride ion. The amounts adsorbed and the interlayer expansions at normalities below precipitation conditions are given in Table III. The influence of multivalent anions on the intrinsic viscosity of variable M.S. HECs is illustrated in Figure 6. The increased amounts adsorbed are within experimental error, but the decrease in d. with the 4.3 M.S. HEC is notable. The d. changes in the absence of increased adsorption are not explainable in terms of solvation effects. 

Determination of trace metals in seawater represents one of the most challenging tasks in chemical analysis because the parts per billion (ppb) or sub-ppb levels of analyte are very susceptible to matrix interference from alkali or alkaline-earth metals and their associated counterions. For instance, the alkali metals tend to affect the atomisation and the ionisation equilibrium process in atomic spectroscopy, and the associated counterions such as the chloride ions might be preferentially adsorbed onto the electrode surface to give some undesirable electrochemical side reactions in voltammetric analysis. Thus, most current methods for seawater analysis employ some kind of analyte preconcentration along with matrix rejection techniques. These preconcentration techniques include coprecipitation, solvent extraction, column adsorption, electrodeposition, and Donnan dialysis. 

For the adsorption of chloride ions on the interface of metallic electrode in aqueous potassium chloride solution, the Gibbs adsorption equation is written as in Eqn. 5-18 ... 

The shift of the potential of zero charge toward the negative direction induced by the contact adsorption of chloride ions has been found not only with liquid mercury electrodes but also with solid metal electrodes such as gold [Jiang-Seo-Sato, 1990]. 

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